276 WHITSBORN DYKE — LEIGH HALL — ROUNDTAIN — TODLETHIR. 



hundred yards of the bedded trap, described p. 271. Other masses of the same origin, consisting 

 of fine crystalline greenstone, appear at the Grimmer Rocks ; these throw off indurated schists on 

 both flanks. Between the Corndon and the hamlet of Priest Weston, is the bold promontory of 

 Llanfawr, throwing off the stratified deposits of Middleton. In this hill there are several varieties 

 of felspar rock, some dark green and veined, which pass into a fine-grained, crystalline greenstone. 



Roundton or Roundtain, a hill, so easily distinguished throughout Montgomeryshire by its round 

 and knotty summit, consists for the most part of an "amorphous mass of greenish-grey, compact 

 felspar, of rough fracture, extremely hard and very slightly porphyritic. It contains carbonate of 

 lime, both disseminated and in small veins, with minute crystals of iron pyrites : one variety is a 

 dark-coloured very fine grained basaltic greenstone. This hill, like its neighbour the Corndon, is 

 precipitous in its east-south-eastern face, and towards the west and south-west, exposes rounded 

 protuberances of trap. One of these varieties at Brith Dir is an amygdaloid of granular felspar, 

 containing kernels of calcareous spar, and resembling a trap rock which occurs at the Cefn, a small 

 southern spur of the Breiddens - } another is a mottled felspar rock, with crystals of common felspar 

 and nests of iron pyrites. 



Todlethir (pronounced Taudley) Hill. — In this hill, and at Symmond's Castle, its south-western 

 termination, I observed 



1. Dark greenstone, approaching to hornblende rock. 



2. Porphyry, having a base of light-coloured compact felspar, with a few imbedded crystals of common felspar and horn- 

 blende. 



3. Pale green porphyritic greenstone, having a tendency to columnar structure. 



4. Greenstone, composed of equal parts of hornblende and compact white felspar, with a few crystals of pink common 

 felspar. 



These are occasionally traversed by veins of carbonate of lime. 



These hills, being direct prolongations of the Corndon, form the central and chief ridge of erup- 

 tion in this district) and their axis extends to the north- north-east through Stapely, by Bromlow 

 Callow to the Grimmer Rocks, where coarse and fine grained greenstones jut out in rugged low 

 protuberances, on the high road between Minsterly and Leigh Hall. The greenstone at Grimmer 

 has a tendency to columnar structure, contains crystals of iron pyrites, and throws off highly in- 

 clined beds of shale to the north-west and south-east. 



The hills of the Rovereas and Squilfa constitute the eastern parallels of the southern part of the 

 district. The Squilfa is composed of coarse grained, light coloured greenstone, partly columnar, 

 the columns rapidly exfoliating at their edges ; it is, in fact, the Corndon in miniature. The Ro- 

 vereas presents, in its western face, also coarse grained greenstone, which differs from that of the 

 Squilfa in containing a greater proportion of dark hornblende and no white felspar. It is flanked 

 on the east by fissile, compact felspar, apparently arranged in vertical beds, which graduate into 

 decided volcanic grit or breccia, similar to that before mentioned ; and still further to the east are 

 the ordinary shale and sandstones of the district. If we try to follow the great basaltiform and 

 irregular masses of greenstone, of the Rovereas and Squilfa in the direction of these ridges to the 

 north-north-east, we soon find, as in the case of the Roundtain and Corndon, that the amorphous 

 rocks suddenly subside, and are succeeded by bedded trap rocks, trending in the same direction. 

 These are first seen in the hill of Cefn Gwynlle, and are prolonged to the north-north-east by the 

 Rynis gate, Pell Radely, Ritton Castle, &c. 1 



1 In a traverse from the Squilfa, by Hyssington to Hurdley, and the flanks of Taudley, we meet with re- 



